BOSTON -- An alarming number of third-graders continue to read below their grade level despite Massachusetts leading the nation on standardized reading assessments, according to a new report.

The study, commissioned by Strategies for Children, a Boston-based nonprofit organization, found that 43 percent of Massachusetts third-graders are still reading below grade level.

The report, written by Nonie Lesaux, a leading expert on literacy at the Harvard Graduate School of Education, states that three-quarters of third-graders with difficulty reading will go on to struggle in high school and be at a higher risk of not graduating. Even those who do graduate may not be ready for college coursework, according to researchers.

"There is a limited window of time in which to prevent reading difficulties and promote reading achievement," Lesaux writes in the report. "For most children what happens -- or doesn't happen -- from infancy through age 9 is critical. By third grade, reading struggles are strongly linked to later school difficulties, as well as behavioral problems, depression, and dysfunctional and/or negative peer relationships."

Locally, six public-school districts -- Ayer, Billerica, Dracut, Lowell, Tewksbury and Tyngsboro -- report that more than 40 percent of their third-graders are reading below proficiency based on 2009 MCAS scores.

In Lowell, 67 percent of third-graders scored below proficient on the MCAS exam.

The report calls for allocating additional resources into effective, early-education reading programs and training teachers to assess reading ability and assist in development.

The study also calls for integrating a more "language-rich" curriculum into early-education classrooms, and forging stronger partnerships with families to improve reading and vocabulary at a young age.

Despite the successes of Massachusetts public schools in national rankings, state education officials have long identified the elementary-school reading scores and a persistent achievement gap between low-income and minority students compared to their peers as causes for concern.

Though the report states that the trend impacts students from urban and suburban districts alike, two-thirds of low-income students do not read at grade level compared with just one-third of their more affluent classmates.

"We have spent a lot of money on reading, but it tends to be scattered. Spray and pray," said Richard Weissbourd, a lecturer at Harvard Graduate School of Education and co-founder of ReadBoston, who serves on the board of Strategies for Children. "We need to capture that energy with more in-depth and intensive work and carefully evaluate programs for effectiveness."